1. Field of the Invention
This invention relates to a complementary amplifier circuit and, more particularly, to a complementary metal-insulator-semiconductor (C-MIS) amplifier circuit comprising a p-channel metal-insulator-semiconductor field effect transistor (referred to as a MISFET or simply as a FET) and an n-channel MISFET.
2. Description of the Prior Art
Complementary field effect transistor amplifier circuits are widely used in electronic circuits, such as an oscillator for an electronic wrist watch. Such a circuit is characterized, for example, by high threshold levels, inherent structural simplicity and low power consumption.
Various types of improved circuits which enjoy the low power characteristics of the complementary FET amplifier have been proposed. For instance, as will be described later, it is possible to connect, through a bias resistor, the gate and drain of each MISFET constituting the complementary amplifier to each other to equalize the gate potential and the drain potential and, at the same time, to connect the drains of two FETs through a load resistor to effect class B operation to reduce the through current and, hence, the power consumption. This type of amplifier circuit is disclosed in the specification of U.S. Pat. No. 4,100,502, entitled "Class B FET Amplifier Circuit" and granted to Osamu Yamashiro. This amplifier circuit, however, requires an operating voltage which is at least equal to or higher than the sum of the threshold voltages of the two MISFETs constituting the complementary amplifier circuit.
In order that a MIS amplifier circuit may operate with an operating voltage which is only higher than the threshold voltage of each of the MISFETs constituting the amplifier circuit, the specification of U.S. Pat. No. 3,887,881 to Kurt Hoffmann entitled "Low Voltage C MOS Amplifier" discloses an amplifier circuit in which two potential divider circuits to each of which a MISFET is connected in series, are connected in parallel with a C-MIS amplifier circuit, the output from the potential divider circuit being applied to the gates of the FETs constituting a C-MOS amplifier. In this amplifier, however, the operating voltage fluctuates undesirably and unstable operation of the amplifier is often caused by fluctuation in the characteristics of the circuit constituents, because the gates of the MOSFETs constituting the C-MOS amplifier circuit are fixedly biased.